This invention relates generally to regulator circuits and more particularly concerns dc regulator circuits utilizing field effect transistors.
Regulator circuits are well known in the prior art and perform the function of providing an output voltage which remains substantially constant as different current levels are drawn from the regulator by a load connected to the output terminal. Also, the output voltage remains substantially constant for a predetermined range of input voltages to the regulator circuit. Typically, prior art regulator circuits use bipolar transistors, and which at low voltage operation are low frequency devices, and typically require at least 1.0 volts (minimum) to operate. This voltage drop results in a power dissipation in the form of heat. Generally these transistors are mounted on heat sinks in order to dissipate the heat built up in the transistor. This is especially true in applications in which high currents are required. The fact that the bipolar transistors require the dissipation of heat determines the physical size requirement of the regulator circuits.
Bipolar transistors have a negative temperature coefficient. Therefore as the bipolar transistor becomes hotter during operation, it will tend to decrease its internal resistance which can result in a runaway situation in which the transistor eventually burns up.
With the advent of field effect transistors, several important properties exist which when used with the present invention result in a significantly improved regulator circuit. One of the properties of importance is that FET's have a positive temperature coefficient, thereby excluding the possibility of a runaway, which in turn allow FET devices to be operated directly in parallel (without balast resistors) for increased output capacity. Also, FET's can be operated with significantly small voltage drop which in turn allows regulator design requiring less power dissipation than bipolar transistors. This also results in less energy loss in the novel regulator circuit of the present invention. Finally the FET has much higher frequency response (at low voltage) than do bipolar transistors which in turn allow designs that require less filtering.